1. Field of the Invention
The present invention relates to a method for the transmission and distribution of digital television (DTV) signals. More particularly, but not by way of limitation, the present invention relates to a method for converting DTV signals to a format for transmission over a communication network, and transmitting the signal via the communication network to a remote location.
2. Background of the Invention
While the quest for high-definition television (“HDTV” or “HD”) has been hampered by the lack of a single standard, resistance by the broadcast industry to implementation, and a substantial price disparity at the consumer level, mandates from the Federal Communication Commission are forcing broadcasters and equipment manufacturers to transition from conventional analog transmission to digital television transmission. These mandates are certain to finally usher in the era of DTV, improving the quality of standard definition television (“SDTV” or “SD”) and advancing the cause of HDTV. As digital programming becomes more prevalent, the need for infrastructure for the production and distribution of digital programming becomes more pressing.
Most of the existing infrastructure was developed for the distribution of analog video, and an assortment of options presently exist as to the production and distribution of analog programming. Distribution via satellite, microwave link, or digitally through a fiber network, or even over conventional wires are common place. Arrangements can be made for a live broadcast from almost anywhere in the world with little more than a few hours notice. Unfortunately, while the video signal may be digitized over some portion of its path, it starts out as an analog signal and is delivered as an analog signal. End-to-end delivery of digital video is just beginning to evolve.
Presently, satellite transponders are available which will carry DTV signals, however the issue of bandwidth is, at best, confusing. Data rates vary widely from satellite-to-satellite and transponder sharing further complicates the issue. A producer who plans on sending a DTV signal via satellite must negotiate bandwidth as well as cost. Regardless of these issues, satellite bit rates for a single transponder are limited to roughly 100 Mbps. As a result, for satellite transmission of DTV, some form of compression is virtually always required. For transmission of HDTV signals via satellite, substantial compression is absolutely necessary. As discussed further hereinbelow, compression raises additional concerns.
Compression techniques can be broadly divided into two categories: 1) lossy techniques; and 2) non-lossy techniques. Generally speaking, lossy compression techniques compress a signal in a manner designed to faithfully reproduce the content at the receiving end while not faithfully recreating the original digital signal. Non-lossy compression techniques faithfully reproduce the original data stream, thus ensuring that the content at the receiving end is identical to that at the transmitting end. Lossy compression techniques have emerged as the standard simply because such schemes provide significantly higher rates of compression over their non-lossy counterparts. Many of the aggressive compression schemes employ forward interpolation which, in terms of video signals, means that the information displayed in the current video frame is at least partially dependent on information contained in one or more future video frames. The result is that these compression techniques, by necessity, add delay to the signal. In general terms, as the data rate increases, the amount of compression decreases and the adverse effects of compression, i.e. fidelity of the output relative to the input and delay, are reduced.
Thus, besides bandwidth and cost, a producer must also ensure a chosen transponder can accommodate the format of the compressed data stream and must determine if the accumulated delays are acceptable, including the transit time between the earth and satellite. The round trip distance from the earth to a satellite alone adds approximately a one-half second delay to a satellite relayed signal.
Like satellite transmissions, for the most part terrestrial infrastructure has been developed around analog video signals. While fiber networks are inherently digital in nature, bit rates offered to video programmers have been driven by traditional quality video. Simply providing more bandwidth to accommodate HDTV signals is hampered by any number of bottlenecks, such as: the data rate supported by the link between a venue and the fiber network, typically supplied by the local telephone company; the link between the fiber network and the receiving end; or even bandwidth limitations of various network elements. At many venues, the link between the venue and the fiber network is actually analog and digitization takes place at the fiber network point of presence. After digitization, even traditional analog video signals are sometimes compressed for digital transmission over the network. As with satellite transmissions, for a given video format, compressing the video signal reduces quality and introduces delay.
Another issue with transmission over terrestrial carriers is reaching multiple receivers. While satellites cover wide areas by their very nature, terrestrial video links tend to be point-to-point. While point-to-multipoint distribution is possible with either wire networks or fiber networks, a route to each receiver must be planned in advance. For live events, program production typically occurs at the venue, while commercials are added at a studio or fixed production facility. Thus the possibility exists that there may be a need for point-to-multipoint delivery both for the original feed from the venue and for the finished programming including commercials. With millions of dollars of revenue on the line, not only does such an event warrant the provisioning of dedicated routes in advance, but also the provisioning of redundant paths to avoid lost programming in the case of a network event such as a fiber cut.
Still another issue in producing and distributing television programming is monitoring the broadcast video, including commercials, at the venue. Even with analog programming, returning finished video to the production truck is problematic. If the finished video is transmitted to network affiliates via satellite, a satellite dish may be used at the venue to receive the signal. Alternatively, if the programming is carried by a local station, the signal can be monitored directly off-the-air. However, local programming may also include locally inserted commercials or content which overlaps the network programming. Yet another alternative is to provision identical infrastructure assets to return the programming as were used to transmit the original signal. This technique could effectively double the cost of distribution.
Yet another issue in the transmission of digital television signals is maintaining synchronization between video and audio portions of the signal. Generally speaking, the delays caused by distance and compression are substantially constant. Once the audio is synchronized to the video, it will stay synchronized. Problems with synchronization arise when the audio signal takes a different path from that of the video signal and the delay in one of the paths is variable, or when the delay introduced through compression is variable.
Thus it is an object of the present invention to provide a system and method for the end-to-end delivery of digital television signals.
Thus it is a further object of the present invention to provide a system and method for the end-to-end delivery of digital television signals with embedded, synchronized audio programming.
It is yet a further object of the present invention to provide a system and method for the end-to-end delivery of digital television signals in a point-to-multipoint environment.
It is yet a further object of the present invention to provide a system and method for the end-to-end delivery of digital television signals via a network conducive to automated provisioning of network resources for a given program.